1. Field of the Invention
This invention relates to a process for producing a semiconductor device module, and more particularly to a process for producing a semiconductor device module such as a solar cell module which is of high-quality and low-cost.
2. Related Background Art
In application to solar cells and epitaxial substrates, there are various advantages on application where a plurality of semiconductor layers having independent regions can be grown on a substrate. In the case of solar cells, a unit cell alone has a low output voltage, and hence commonly a plurality of unit cells are often connected in series when used. In thin-film solar cells such as amorphous silicon solar cells, semiconductors deposited on one sheet of substrate can be formed dividedly and connected in series on the substrate, thus production efficiency can be improved.
In the case of crystal solar cells, however, such a manner of connection has ever been impossible. Accordingly, after junctions and electrodes are formed in unit cells, the unit cells are connected in series to form a module. This manner of connection makes it necessary to repeat like steps many times, and is complicated in production especially in the case of small-sized modules. Also, in the case of epitaxial substrates, a large number of unit devices such as transistors are fabricated on the substrate. In order to electrically separate these unit devices from one another, it is desirable as an ideal means to provide insulating layers between the devices, where, in a conventional method, high-density doped regions are provided between devices or between the substrate and the epitaxial layer to form junctions. Such a conventional method, however, requires fairly complicated steps to provide such high-density doped regions.
Japanese Patent Application Laid-Open No. 11-68133 discloses a process for producing a solar cell module, in which the surface of a single-crystal silicon substrate is made porous to form a porous layer (a separation layer), a plurality of solar cell devices are formed thereon, thereafter the single-crystal silicon substrate (with the porous layer and solar cell devices) is bonded to a film substrate through an adhesive, the substrates thus bonded are separated at the porous layer to transfer the plurality of solar cell devices to the film substrate, then this film substrate is separated to provide a plurality of solar cell devices, thereafter these solar cell devices are mounted on a supporting film substrate, and the solar cell devices are electrically connected to one another to produce the solar cell module. Japanese Patent Application Laid-Open No. 11-31827 also discloses a process in which a plurality of solar cell devices insulatingly separated from one another are separated from a substrate and thereafter connected in series.
However, the production process disclosed in Japanese Patent Application Laid-Open No. 11-68133 has many steps since the solar cell devices are separated after they are transferred to the film substrate, and are further mounted on the supporting film substrate and then connected electrically. Also, the process disclosed in Japanese Patent Application Laid-Open No. 11-31827 has a narrow freedom of design in the step of forming wirings at the time of series connection.
An object of the present invention is to provide a production process preferable for producing a semiconductor device module, in particular, an integrated series-connected solar cell module, which can be produced by a simple process.
The semiconductor device module production process of the present invention comprises the steps of:
forming a first substrate having a separation layer having thereon a plurality of independent semiconductor layers and semiconductor devices individually formed on the plurality of semiconductor layers;
electrically connecting the semiconductor devices one another on the first substrate; and
separating the plurality of semiconductor layers from the first substrate at the separation layer to transfer the semiconductor layers to a second substrate.
The semiconductor device module production process of the present invention is also characterized in that, in the above semiconductor device module production process of the present invention, the first substrate is subjected to a process having at least the step of forming a cover layer for blocking the growth of the semiconductor layers, on the surface of a semiconductor substrate at its region except the regions where the semiconductor layers are to be formed, and the step of bringing the semiconductor substrate having the cover layer formed thereon, into contact with a melt saturated with a semiconductor material to cause the semiconductor layers to grow in the regions where the semiconductor layers are to be formed.
In the present invention, the semiconductor devices are electrically connected one another before the plurality of semiconductor layers are transferred to the second substrate. This enables use of a process requiring a heat treatment step, and enables connection by thin-film processing. As a result, it is able to produce a semiconductor device module whose device-separated semiconductor layers can electrically be connected with ease, in particular, a solar cell module which enables integrated series connection with ease in spite of crystal type solar cells.